1. Field of the Invention
The present invention relates to rotating electric motors.
2. Description of the Background Art
Conventionally, a permanent magnet type motor having a permanent magnet disposed at the rotor is employed in various fields, and used as a driving source for electric vehicles and hybrid vehicles.
For the driving source of such electric vehicles and hybrid vehicles, the vehicle running performance of low revolution-high power and high revolution-low power is required.
The torque produced by the motor generally depends upon the magnetic flux flowing to the stator from the rotor and the armature current flowing to the stator winding.
The magnetic flux flowing across the stator and rotor is determined by the employed magnet and the like. The magnetic flux is maintained constant independent of the rotational speed. The rotational speed is determined by the armature current. However, since the armature current is determined depending upon the voltage from the power source such as an inverter, the speed of revolution becomes highest when the voltage of the armature winding matches the maximum voltage of the power supply voltage.
When constant power driving is to be conducted based on a constant power supply voltage in such a permanent magnet type motor, there is known the so-called “field weakening” and “field strengthening” for the purpose of further increasing the highest speed of revolution to improve the running performance as well as to increase the power at a low revolution speed, as disclosed in Japanese Patent Laying-Open Nos. 6-351206, 2002-78306, 2005-65385, and 7-288960; “Some Considerations on Simple Non-Linear Magnetic Analysis-Based Optimum Design of Multi-pole Permanent Magnet Machines” by Yoshiaki Kano, Takashi Kosaka, and Nobuyuki Matsui in IEEJ Trans. IA, Vol. 123, No. 3, pp. 196-203 (2003); and “Some Investigations into Performance of Hybrid Motor with Novel Construction” by Jin Zheguo, Takashi Kosaka, Nobuyuki Matsui in the Proceedings of National Conference of the IEE of Japan 2005.
For example, the motor disclosed in “Some Considerations on Simple Non-Linear Magnetic Analysis-Based Optimum Design of Multi-pole Permanent Magnet Machines” by Yoshiaki Kano, Takashi Kosaka, and Nobuyuki Matsui in IEEJ Trans. IA, Vol. 123, No. 3, pp. 196-203 (2003) includes a rotor divided into two in the axial direction, a ring magnet arranged between the divided rotors, a field pole formed of a powder-molded magnetic composite arranged at the outer circumferential side of the stator core, and a toroidal field coil.
The divided rotors include a plurality of salient poles formed along the circumferential face spaced apart from each other. The salient poles are arranged such that the salient pole of one rotor is displaced with the salient pole of the other rotor in the circumferential direction.
The N magnetic pole of the ring magnet is arranged towards the end face of one divided rotor whereas the S magnetic pole is arranged towards the end face of the other rotor. The magnetic line of force from the ring magnet first enters the rotor from the end face thereof and runs through the air gap from the salient pole of one rotor towards the stator. Then, the magnetic line of force from the stator passes through the field pole to run from the stator teeth to the salient pole of the other divided rotor via the air gap to return to the S magnetic pole of the ring magnet.
Then, using a toroidal field coil, the magnetic flux of the permanent magnet is drawn towards the field pole, reducing the magnetic flux passing through the armature winding. Thus, field weakening is realized. Furthermore, the magnetic flux of the permanent magnet is confined in the main motor, so that the magnetic flux generated by the toroidal field coil increases the magnetic flux passing through the armature winding to realize field strengthening.
In the rotating electric motor set forth above, the magnetic line of force exits the salient pole of one of the divided rotor, and the magnetic line of force enters the salient pole of the other divided rotor. Therefore, each region of the rotor located between the salient poles will not contribute to torque generation. There was the disadvantage that the rotor must be increased to obtain the desired torque.
There is also the disadvantage that the magnetic line of force, when entering the salient pole of the rotor, is affected by the magnetic flux of the armature winding. As a result, the magnetic line of force from the stator will not enter the desired salient pole. There was a problem that negative torque is generated, depending upon the direction of the magnetic line of force.